1. Field of the Invention
The present invention is broadly concerned with an improved method and apparatus for heating, packaging and sterilization of pumpable particulate food products under closely controlled temperature and pressure conditions which eliminate overcooking and flashing of the product with consequent beneficial effects on the organoleptic properties of the products. More particularly, it is concerned with such a method and apparatus making use of a pressurized packaging chamber in direct, open communication with a product delivery line, so that the superatmospheric chamber pressure provides back pressure for the product line; in this fashion, the easily controllable filling chamber pressure assures essentially plug product flow and a substantially uniform, decreasing pressure gradient throughout the length of the product conduit.
2. Description of the Prior Art
The canning and retorting of food products such as soups, stews, chilies and other items are conventional and well established processes. A common complaint about such canned foods, however, resides in the unnatural flavor attributable to the canning and retorting process. That is to say, it is absolutely essential that such products be adequately sterilized to avoid spoilage, and as a consequence processors have tended to effectively overcook the products in order to assure proper sterilization. This in turn creates the overcooked, unnatural flavor characteristic of so many canned items.
U.S. Pat. No. 3,241,475 describes a canning procedure somewhat different than the conventional technique. The method and apparatus described in this patent has been commercialized for a number of years as the so-called "Flash 18" process. In this technique, a food to be processed is first pumped through a pair of series-connected upstream lobe-type feed pumps, whereupon the product passes through either an indirect heat exchange cooking unit or a zone of steam injection. Thereupon, additional moisture may be added to the product and it passes through yet another lobe-type back pressure pump. At this point, the product may pass through a flash deaerator in order to lower the product pressure and temperature, whereupon the product passes through a fourth lobe-type pump and is directed to a packaging chamber. The packaging chamber itself is in the form of a relatively large, pressurized building accommodating canning equipment and plant personnel. In the chamber, product from the deaerator is canned in the usual fashion, and is then sent to a sterilizing and cooling station exteriorly of the chamber.
While the described "Flash 18" process has been in use for a number of years, it presents a number of problems from the standpoint of product integrity, particularly in the case of large particulate products. Specifically, the use of multiple lobe-type pumps for propelling the product through the processing line and establishing back pressure therewithin inevitably creates substantial pressure variations and a non-uniform pressure gradient throughout the product line. As a consequence, in order to avoid premature flashing of the product, there must be a substantial pressure differential between the steam pressure within the indirect heat exchange jackets or as injected, and the product pressure. In practice, this pressure differential has been in the range of 15 to 20 p.s.i.g. Furthermore, inasmuch as this relatively high pressure differential is established within the product line, in most instances it is necessary to flash deaerate product prior to entering the pressurized filling chamber. Such deaeration of course presents another zone of rapid pressure change within the product line upstream of the filling chamber, and can in and of itself detract from particulate integrity.